This project consisted of three studies, two of which examined the effects of moisture deficits and moisture stress conditioning of black alder seedlings and the third examined the effects of shoot manipulations on the physiology of black alder seedlings and the nitrogenase activity of the seedlings' root nodules. Endophyte strain was found to be nonsignificant in response to moisture deficit and moisture-stress conditioning (MSC). Using regression analysis MSC significantly decreased the impact of low water potentials on photosynthesis and acetylene reduction. There were no significant improvements in this response with increased MSC periods. Exposure of nodules to dry soil conditions while keeping the host plant hydrated did not significantly reduce acetylene reduction, nodule sugar content, transpiration or leaf conductance; however, photosynthesis was significantly reduced. Only defoliations of 100% significantly lowered acetylene reduction. Defoliations of 45% caused increases in photosynthesis and transpiration of residual leaves three days following defoliation. Nodule sugar content was unaffected by any level of defoliation. / Master of Science